Apache is a free and open-source cross-platform web server software.
PayPal is an online payments system that supports online money transfers and serves as an electronic alternative to traditional paper methods like checks and money orders.
vBulletin is tool that is used to create and manage online forums or discussion boards. It is written in PHP and uses a MySQL database server.
YUI is a JavaScript and CSS library with more than 30 unique components including low-level DOM utilities and high-level user-interface widgets.